This invention relates to a rotary electric machine, for example, a synchronous machine having salient rotary magnetic poles. More particularly, it relates to a rotary electric machine equipped with a so-called built-up type rotor in which a plurality of rotary members are coupled in the axial direction into an integral form.
In general, the built-up type rotor is split in a plurality of rotary members in order to avoid inconveniences in the fabrication and in the transportation of the rotor as are attendant upon a large-sized structure. To this end, the rotary members are respectively and individually fabricated, and the individual members are transported in separate forms. At the installation site, the respective rotary members are then coupled in the axial direction so as to build up the rotor. For further discussion of this subject, refer to U.S. Pat. No. 3,780,428 and "The Brown Boveri Review", Vol. 52, No. 1/2, page 34, FIG. 46.
The coupling faces of the rotary members of such a split rotor are formed into surfaces at right angles to the axial direction, and the rotary members are integrally coupled by means of clamping bolts. In addition, in order to facilitate assembling the rotary members coaxially with one another and to prevent the rotary members from being displaced in the radial direction from one another, the respective rotary members are provided on radially inner sides thereof with faucet joints for snugly fitting the adjacent rotary members to each other.
On the outer periphery of the split rotor thus constructed, magnetic poles (consisting of a field core and a field winding) are mounted to form rotary magnetic poles in the case of, for example, a synchronous machine, and a field winding is assembled by providing a winding groove in the case of, for example, a turbo-generator.
In the case where such a built-up type rotor is comparatively small-sized and is rotated at low speed, it carries out a stable rotation without undergoing radially outward displacements among the rotary members. However, in the case where the machine size becomes large with increase in the capacity of the rotary electric machine and the speed becomes high, the radially outward displacements of the rotary members cannot be suppressed by only the frictional forces of the coupling faces and the faucet joints between the adjacent rotary members as described above. The rotational balance of the split rotor therefore collapses due to the radially outward displacements of the rotary members, so that oscillations occur. The oscillations cause the built-up type rotor, and in turn, the whole rotary electric machine, to be subject to damage.
More specifically, when the split rotor is large-sized, naturally the respective rotary members are large-sized. When the rotor rotates at high speed, the respective rotary members are stretched by centrifugal forces. If the degree of stretching is equal for all the rotary members, the symmetry of the rotor will not be affected and the rotational balance will not be impaired. Due to differences in the frictional force between the adjoining rotary members and in the shapes of the respective rotary members, however, the degree of stretching of the individual rotary members is generally not equal, so that the rotary members are displaced by different amounts. If the stretching directions of each rotary member are basically the same over the entire circumference thereof, the rotational balance will not be seriously affected even when the adjacent rotary members are subject to slight differences in displacement. In practice, however, the stretching directions are not uniform over the entire circumference, but appear in irregular directions on account of the aforecited differences in the frictional forces and in the shapes of the respective rotary members. The non-uniform displacements break the rotational balance, and form the basic cause of the oscillations which result in ultimate damage to the machine.